It has been known that, in a concrete structure such as a tunnel and a bridge, a crack formed on the surface of the structure has an influence on the soundness of the structure. Therefore, in order to accurately determine the soundness of the structure, it is necessary to accurately detect a crack.
As a method for detecting a crack, for example, there is a method for detecting a crack by visual observation. However, accuracy of detection of a crack by visual observation depends on the ability of a person who performs visual observation. Therefore, it may not be possible to accurately detect a crack according to the ability of a person who performs visual observation. As described above, the method for detecting a crack by visual observation has a problem that it depends on the ability of a person. In this regard, there have been proposed various technologies that allow for detecting a crack regardless of the ability of a person, in addition to the detection of a crack by the visual observation.
For example, a technology for binarizing an image captured by a capturing means by a predetermined threshold value and detecting an image part corresponding to a crack from the image for a structure is proposed, as a first related art to the present invention (for example, see Patent Literature 1).
Furthermore, a technology for capturing a structure by using a capturing means a plurality of times while changing an angle of a light source that lights the surface of the structure, comparing pixel values of the same measurement target parts of each image with each other, and detecting a crack image is proposed, as a second related art to the present invention (for example, see Patent Literature 2).
Furthermore, a technology for removing a low frequency component of an image obtained by capturing a structure, by using wavelet transformation, creating binary image data by removing spots and stains with small spatial variability from the surface of the structure, and detecting a crack image from the binary image data is proposed, as a third related art to the present invention (for example, see Patent Literature 3).